The soda can will provide the material for the pinhole. The advantage of this is that you can make different pinholes and swap them out of the camera body. Different hole sizes will produce different effects. Also, making the edges of the pinhole jagged will create a "rough edged" photo you take with the camera. Also, if you mess up, you can have a second chance.
Cut a small square out of the soda can (can be any dimension, but must cover the 1/8 hole in the tin), and find the center of the square using the ruler.